Capacitor with decreased flammability

ABSTRACT

A capacitor of the regenerative type having decreased flammability. The capacitor employs as the dielectric fluid a hydrocarbon to which has been added a mixture of perfluorinated hydrocarbons.

I United States Patent l 1 1 1111 3,786,324 Kotschy l l Jan. I5, 1974CAPACITOR WITH DECREASED FLAMMABILITY [56] References Cited [76]Inventor: Josef Kotschy, Kreillerstrasse 68, UNITED STATES PATENTSMunich, Germany 2,433,729 12/1947 Bennett 252/66 X [22] Filed: May 4,1973 Primary ExaminerE. A Goldberg [211 357,326 Attorney-Carlton Hill etal.

[30] Foreign Application Priority Data [57] ABSTRACT May 1972 Germany P22 22 6999 A czipacitor of the regenerative type having decreasedflammability. The capacitor employs as the dielectric [52] US. Cl317/258, 252/81, 252/66 fluid a hydrocarbon to which has been added a[51] Int. Cl H01g 3/215 ture of perfluorinated hydrocarbons. [58] Fieldof Search 317/258, 260; 252/66 18 Claims, 3 Drawing Figures ,lill

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CAPACITOR WITH DECREASED FLAMMABILITY BACKGROUND 1. Field of theInvention This invention relates to electrical capacitors and especiallyto regenerative capacitors using hydrocarbon liquid impregnating agentscontaining a relatively small amount of a perfluorinated hydrocarbonmixture.

2. Prior Art Liquid impregnated, regenerative type capacitors aresubject to use conditions under which the capacitor interior experiencesinflammatory conditions from sparks and/or heat. While the danger offire in nonregenerating condensers can be very substantially re duced byusing relatively inexpensive, nonor almost non-flammable, impregnatingsubstances containing chlorine (such as chlorinated diphenyls), suchsubstances cannot be used in regenerative-type capacitors because thedisintegration products from such substances produced by discharge andregeneration cycles in regenerative type capacitors so severly andadversely affects electrical properties of such capacitors that they canbe rendered inoperative after only one or a few such cycles.

Fluorinated hydrocarbons may be used advantageously in regenerative typecapacitors in place of chlorinated hydrocarbons, but such materialspresently generally are commonly at least about 100 to 300 times moreexpensive than the older, non-halogenated capacitor impregnating organicliquids which limits their practical usage in regenerative capacitors.

In an effort to reduce the flammability characteristics of regenerativecapacitors and still use largely only conventional impregnating fluids,it has heretofore been proposed to add a relatively small amount of aperfluorinated hydrocarbon type material to a nonhalogenatedhydrocarbon-type dielectric impregnating fluid. The resultingtwo-component mixture has reduced flammability characteristics comparedto such a conventional hydrocarbon fluid used alone. Such a resultingmixture, however, has been found to suffer from the very real andsignificant disadvantage that inflammability of such mixture is onlydecreased over a limited temperature range for a limited time,apparently because the vapor pressure of the fluorocarbon additive is afunction of temperature. The obvious technique of overcoming thisdisadvantage through addition of larger amounts of fluorocarbon additiveis economically impractical.

There has now been discovered, however, a technique which unexpectedlyand surprisingly enables one to reduce flammability of a conventionaltype dielectric impregnating fluid for relatively prolonged periods oftime over relatively large temperature ranges. This technique involvesadding to such a conventional impregnating fluid a mixture of twodifferent types of fluorocarbon materials. The amount of such mixtureemployed in any given such product fluid composition may be relativelysmall which makes the technique economically practical. The overallreduction in flammability characteristics thus achieved by adding such amixture to a conventional impregnating fluid is greater than thatachieved by using either of the two types of fluorocarbon materialsalone in equivalent amounts under comparable conditions with such aconventional fluid. Indeed, the coaction between the componentfluorocarbon material types in such a mixture in admixture with such aconventional impregnating fluid in regenerative capacitor useenvironments is such that a synergistic effect can be considered to beinvolved.

The result is a new and improved class of regenerative capacitors usingsuch fluids which have highly desirable flammability characteristicscompared to prior art capacitors employing only conventional hydrocarbontype impregnating fluids alone or in combination with a singlefluorocarbon material.

SUMMARY OF THE INVENTION This invention is directed to a capacitor ofthe regenerative type adapted to have decreased inflammability. Thiscapacitor has a gas tight and liquid tight housing. In this housing,there is positioned at least one capacitive element. Each capacitiveelement in the housing comprises alternate, wound layers of adielectricum sheet member comprising a synthetic material such aspolyolefin interposed between a pair of electrically conductive sheetmembers, each conducting sheet member comprising a metalized paper sheetof which at least one is regenerable.

Spacer means are provided which are adapted to maintain the capacitiveelement or elements in spaced, electrically separate relationship tosaid housing.

A pair of electrical current conduit means are provided which both passthrough such housing. One of such conduit means interconnects, in eachcapacitive element, with one of such conductive sheet members, while theother of such conduit means interconnects, in

each capacitive element, with the other of such conductive sheetmembers.

A dielectric fluid adapted to impregnate such electri cally conductivesheet members in each such capacitive element is present within suchhousing. Such fluid is so present in a quantity at least sufficient toimpregnate and to surround such capacitive element or elements and alsoto form an excess thereabove with a vapor space above the level of suchfluid in said housing when said capacitor is in a functional positionspatially. The vapor space is saturated with the vapors of said fluid,as those skilled in the art will appreciate.

In a capacitor, each such capacitive element is adapted for selfregeneration of its capacitive capability in the event of a failurethereof in response to electrical energy applied to said conduit means.

The dielectric fluid itself comprises in homogeneous combination amixture of a hydrocarbon liquid with a relatively small amount of aperfluorinated fluorocarbon liquid mixture. Thus, the hydrocarbon liquidhas a boiling point in the range of from about 250 to 300C. Preferredexamples of such a liquid include mineral oil (which here mostpreferably comprises about 56% paraffinic constituents, about 29%napthalenic constituents, and about 15% aromatic constituents),dodecylbenzene, dioctylsebacate, and the like.

The liquid fluorocarbon mixture comprises at least one firstfluorocarbon selected from the group consisting of trifluoromethylperfluorohydrooxazine and perfluorinated dimethylcyclohexane, and atleast one second fluorocarbon selected from the group consisting of aperfluoroalkylpolyether which has a boiling point of about 152C., aperfluoroalkylpolyether which has a boiling point of about 194C, andtrifluoromethyl perfluorodecalin. In a given such fluorocarbon mixture,the weight ratio of said first fluorocarbon to said sec- 250C. and about300C.

DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 illustrates the combustion protection duration t in seconds for amineral oil of approximately 56 weight percent paraffinic components, 29weight percent naphthalenic components, and weight percent aromaticcomponents admixed with varying amounts of trifluoromethylperfluorodecalin of each of two different temperatures, namely 200C. and300C.;

FIG. 2 shows the minimum amount V,,,,,, of perfluorinated liquid neededfor combustion protection of mineral oil of the type used in FIG. 1compared to the ratio T,/T where T, is the boiling temperature ofperfluorinated liquid and T that of the mineral oil; and

FIG. 3 is a side elevational, diagrammatic, schematic view of anembodiment of a regenerative condensor utilizing the principles of thepresent invention.

DETAILED DESCRIPTION Referring to FIG. 1, it is seen that the additionalamount of trifluoromethyl perfluorodecalin needed for a short combustionprotection T becomes lower as the temperature of the impregnation fluidincreases. Therefore, for a combustion protection duration of, forinstance, about five seconds at about 200C., three Vol per mil isrequired; however, at about 300C. only 0.3 Vol per mil of suchadditional liquid is required. Totally different conditions prevail ifalonger combustion protection duration is required. For a protection timeof, for instance, approximately 60 seconds at a temperature of about200C, an addition of six Vol per mil is required while at about 300C. anaddition of 100 Vol per mil is required. The different attitudes can betraced back to the fact that, for a short term protection effect, thetemperature dependency of the vapor pressure of the additional liquid isdeterminative, whereas the protective duration for a longer termprotective effect is limited by the evaporation speed. As can be seenfrom FIG. 1, for the effective combustion protection of mineral oilinsulation liquid even at low temperatures, considerable amounts of thenon-flammable substance trifluoromethyl perfluorodecalin are required.

A number of further perfluorinated liquids with boiling points withinthe range from 50 to 195C. were examined individually as regards theirability to reduce the flammability of insulation oil. These included N-trifluoromethyl perfluorohydrooxazine, perfluorinated1,4-dimethylcyclohexane, and two perfluoroalkylpolyethers, one with aboiling point of 152C, the other, 194C, as well as the already mentioned1- trifluoromethyl perfluorodecalin. The following Table 1 shows theminimum amounts V,,,,,, of these perfluorinated liquids needed to avoidinflammation of a mineral oil comprising approximately 56 weight percentparaffinic parts, 29 weight percent naphthalenic parts and 15 weightpercent aromatic parts for a combustion protection duration of 5 secondsin the range of 200 to 300C.

As can be seen from Table l, the additional amount of perfluorinatedcompound needed for avoidance of inflammation (combustion) becomeslarger the lower the temperature of the insulation oil and the higherthe boiling point of the perfluorinated liquid.

The combustion protection time t,; for the same mineral oil as used inTable 1 mixed with specified perfluorinated liquid at the rate of 10 Volper mil in the temperature range of 200 to 300C. is shown in thefollowing Table 2.

As can be seen from Table 2, the combustion protection duration tdecreases with increasing temperature of the mineral insulation oil at aconstant content of perfluorinated liquid. For some substances, however,it is found that the combustion protection duration increases withrising boiling point whereas such value here decreases for theperfluoroalkylpolyether with a boiling point of 194C. This is perhapscaused by the fact that fewer molecules of the latter material go intothe vapor phase than with the former such materials as the boiling pointrises with the result that the combustion protection duration decreasesfor the latter material at some temperature.

FIG. 2 shows the minimum amounts (V,,,,,,) of added perfluorinatedmaterial needed to guarantee a combustion protection of 5 seconds forvarious perfluorinated materials logarithmically expressed as functionof the reciprocal value of the ratio of mineral oil temperature T to theboiling temperature T, of the respective added perfluorinated liquid.The vaious added perfluorinated liquids are provided with the numerals lto 5 which corresponds to the compound designations used Tables I and 2.As FIG. 2 demonstrates, the measured points for mixtures of mineral oilwith perfluorinated liquid lies approximately on the straight linerepresented by the equation:

In V min const. (T /T).

It follows from FIG. 2 that in order to achieve an equivalent result,the additional amount of added perfluorinated liquid has to be larger,the higher the boiling point T, of the added perfluorinated compound andthe lower the boiling temperature T of the impregnating liquid (heremineral oil). In the case where T equals T,,, this means that if theboiling temperature T, of the perfluorinated compound and the boilingtemperature T of the impregnating liquid are equal, approximately 10 Volper mil of the protective substance (here perfluorinated hydrocarbon) isrequired for a combustion protection duration of5 seconds. It is alsolearned from FIG. 2, that, in case of a perfluorinated liquid whichboils at about 0.8 times the amount of the boiling temperature T of theimpregnating liquid, only an additional amount of about 1 Vol per mil ofperfluorinated liquid is required to achieve the same combustionduration protection.

It seems at first as though T, should be chosen as low as possible inorder to achieve as low an additional amount as possible. However, itshould be taken into consideration that the evaporation speed stronglyincreases if the boiling point T, of the perfluorinated additionalliquid lies considerably below the boiling temperature T of theimpregnating liquid. 'lhis, huwcvcl,

means that, when a capacitor is destroyed, the combustion protectionduration becomes lower the smaller the ratio T,/T.

For economic reasons, the combustion avoidance of the impregnation agentshould be achieved with as little additional amounts of a perfluorinatedliquid as possible. However, with only one substance according to theabove described facts this cannot always be sufficiently realized sinceliquids with a low boiling point do guarantee already at a lowconcentration a sufficient vapor density but evaporate at hightemperature with too much speed so that a sufficient combustionprotection duration for a capacitor is not guaranteed. Liquids withhigher boiling points have too low a vapor pressure at low temperaturesto guarantee a sufficient protection duration for commercialpracticality. Therefore, in accordance with the discovery of the presentinvention, it is advantageous to add a mixture of two different types ofperfluorinated liquids each type having a different boiling temperatureT,, to a hydrocarbon liquid used to impregnate a regenerative capacitor.Thus, for example, when as the lower boiling perfluorinated compound oneuses N-trifluoromethyl perfluorohydrooxazine (boiling point 50 to 60C.)and as the higher boiling perfluorinated compound one usestrifluoromethyl perfluorodecalin (boiling point 160C.) and adds themixture to a mineral insulation oil of the type hereinabove described,the combustion point of this mimeral oil, which normally has acombustion point of about 185C. and a (boiling) vaporization point ofabout 300C., is unexpectedly raised and the combustion protection timeis unexpectedly expanded.

As can further be learned from Table l, the minimum protective amountV,,,,,, which guarantees a combustion protection time of 5 seconds in animpregnating fluid mixture using trifluoromethyl perfluorohydrooxazineat an oil temperature of about 200C. is about 0.5 Vol per mil of mineraloil hydrocarbon liquid. Also, 0.5 Vol per mi] of trifluoromethylperfluorodecalin with mineral oil is required in order to guarantee atabout 300C. the same combustion protection time t,,. The ratio of thetwo respective perfluorinated liquids is in this case 1 to 1. If otherinflammable liquids or other hydrocarbon liquid impregnating fluids, areused, it will be appreciated that the optimum amount of perfluori-'nated liquid added to hydrocarbon liquid will vary, depending oncircumstances, such as the liquids involved, and the amount ofcombustion protection duration desired, and the like, so that it is nothere possible to give a simple indication of relative amounts that willbe applicable to all the use situations contemplated by the teachings ofthe present invention.

If, for instance, a hydrocarbon liquid is used whose combustion pointlies at a lower temperature than that of the above mentioned mineralinsulation oil, that is, lower than about 185C., it is advisable, if oneis using the same perfluorinated hydrocarbons, such astrifluoromethylperfluorohydrooxazin and trifluoromethylperfluorodecalin,to add more of the lower boiling perfluorinated hydrocarbon; forexample, up to a ratio of the two liquids -1.5 0.5 of substitutedoxazine to substituted decalin. The reverse applies if the hydrocarbonliquid has a higher combustion point than about 185C. in which case, ifone likewise uses these same liquids, it is advisable to use more of theless volatile substance (here the substituted decalin), as in a ratio of0.65 1.3 of substituted oxazine to substituted decalin.

Decisive for the duration of the combustion protection is the amount ofperfluorinated liquid which is added to the hydrocarbon liquid. Thedesired combustion protection duration 1,, for a given capacitor depends on the application purpose of that capacitor. Thus, for example,if several seconds only are desired, it is sufficient that the total ofthe amounts of the two liquids (the substituted oxazine and thesubstituted decalin) be present with the hydrocarbon liquid at a ratioas low as about 0.00025 1. For longer protective times, it can benecessary to extend this ratio up to 0.1 l or even higher, depending onthe use conditions.

Turning to FIG. 3, there is seen an exemplary embodiment of aregenerative capacitor incorporating the principles of the invention. Acapacitor 1 includes a cup shaped housing or container means 1 havingwound capacitor elements 2 positioned in working relation therein. Thecapacitor elements 2 include wound, alternating layers of metal foilelectrode and impregnated intermediate layers and/or dielectric layers.The wound capacitor elements 2 have a central core hole 3. Animpregnating fluid mixture 4 completely surrounds the capacitor elements2 and forms an excess above the capacitor elements. Area 5 above theimpregnating liquid comprises the vapor space and is saturated with thevapors of the impregnating liquid 4.

The housing means is sealed with the cover member 6. A sealing ring 8 isprovided along the peripheral edges of cover member 6 and is biasedagainst the cover member. Flange-like portions 7 of the housing means lamaintain the sealing ring 8 and cover member 6 in substantially vaporimpermeable relation on the housing. Electrical current conduits ofopposite polarity 9 and 10 are passed through the cover member 6 forconnection to electrical circuitry as desired. The wound capacitorelements 2 are supported from the buttom of housing means 1 by cam-likemembers 11 and and are held in spaced relation from the wall thereof bya lateral cam-like member 12. Of course, except for the impregnatingfluid, other regenerative capacitor constructions may also be utilizedas those skilled in the art will appreciate in practicingthe presentinvention. For example, cam-like member 12 may comprise a plurality ofsuch cam-like members, as well as other suitable reinforcement means.Whatever means are utilized to position the wound capacitor elements ina working relation within a housing means, the impregnating liquid orimpregnating liquid mixture must be capable of omnidirectionalenvelopment of the capacitor elements. i

In a capacitor 1, each capacitive element typically utilizes as adielectric layer a polyolefin film, preferably a polypropylene film, oneither face of which is located a metallized paper web or sheet. Thesethree layers, or foils, are spirally wound together to form the desiredelement. The conducting wires are then mounted on each one of themetallized webs.

The impregnating dielectrical fluid saturates the paper sheet members sothat small amounts of the impregnating fluid leak into the polyolefinoil through the thin metallized sheet members and makes the polyolefinfoil swell. By means of such swelling such foil conforms to themetallized paper webs closely so that there is achieved a capacitorhaving a high dielectric strength. The virtual absence of air spacesbetween the layers also prevents the development of undesirable strayvoltages. Range spaces are not necessary.

In general, preferred hydrocarbon liquids for use in the presentinvention have a combustion point in the range from about 140 to 270C.Also, preferably a given perfluorinated liquid, which is used incombination with a particular hydrocarbon liquid in accordance with theteachings of this invention, has a boiling point which is at least about50C. lower than the boiling point of that hydrocarbon liquid, and, morepreferably, about 100C lower. In general, any hydrocarbon liquid havinga boiling point in the range indicated, and also having a combustionpoint in the range indicated, may be used in the practice of the presentinvention, as those skilled in the art will appreciate, althoughpreferably a hydrocarbon liquid has a dielectric constant in the rangeof from about 1.7 to 3.8, as shown in the Examples. The term hydrocarbonas used herein in reference to an impregnating liquid adapted for use inregenerative capacitors, as those skilled in the art will appreciate, isemployed in its broad generic sense to connote any organic compoundhaving characteristics as indicated, which comprises carbon andhydrogen, and which may also contain oxygen, as for example, in the formof ether linkages, carbonyl groupings, or the like.

Those skilled in the art will appreciate that by suitable selection ofhydrocarbon liquid and liquid fluorocarbon mixture, in accordance withthe teachings of this invention, the duration of combustion protectionof at least about seconds can be broadened so that the protectiontemperature range for such 5 second interval can be extended outwardlybelow 250C. Thus, for instance, in Example 2 below, this range goes downto 180C while, in Example 1, this range goes down to 150C.

A combustion protection duration of at least about 5 seconds at each of150C and 300C is thus achieved by using as the dielectric fluid onewherein the hydrocarbon liquid is dodecylbenzene, the liquidfluorocarbon mixture comprises as said first fluorocarbontrifluoromethyl perfluorohydrooxazine, and said second fluorocarbon isselected from the group consisting of a perfluoroalkylpolyether whichhas a boiling point of about 152C and trifluoromethyl perfluorodecaline.

Similarly, combustion protection duration of at least about 5 seconds ateach of about 250C and about 300C is thus achieved by using as thedielectric fluid one wherein the hydrocarbon liquid is dioctylsebacate,and the liquid fluorocarbon mixture comprises as said first fluorocarbonperfluorinated dimethylcyclohexane and said second fluorocarbon isselected from the group consisting of a perfluoroalkylpolyether whichhas a boiling point of about 152C. and a perfluoroalkylpolyether whichhas a boiling point of about 194C.

Preferably, in a capacitor of this invention, the fol lowing dielectricfluid systems may be used:

A. A fluid wherein said first fluorocarbon is N- trifluoromethylperfluorohydrooxazine and said second fluorocarbon is aperfluoroalkylpolyether which has a boiling point of about 152C.

B. A fluid wherein said first fluorocarbon is trifluoromethylperfluorohydrooxazine and said second fluorocarbon is aperfluoroalkylpolyether which has a boiling point of about 194C.

C. A fluid wherein said first fluorocarbon is trifluoromethylperfluorohydrooxazine and said second fluorocarbon is trifluoromethylperfluorohydrooxazine.

D. A fluid wherein said first fluorocarbon is perfluorinated 1.4-dimethylcyclohexane and said second fluorocarbon is aperfluoroalkylpolyether which has a boiling point of about 152C.

E. A fluid wherein said first fluorocarbon is perfluorinated 1.4dimethylcyclohexane and said second fluorocarbon is aperfluoroalkylpolyether which has a boiling point of about 194C., and

F. A fluid wherein said first fluorocarbon is perfluorinated 1.4-dimethylcyclohexane and said second fluorocarbon is trifluoromethylperfluorodecalin.

EMBODIMENTS The present invention is further illustrated by reference tothe following examples. Those skilled in the art will appreciate thatother and further embodiments are obvious and within the spirit andscope of this invention from the teachings of these present examplestaken with the accompanying specification and drawings. All parts areparts by weight, unless others were indicated.

In the present examples, as well as elsewhere in the present invention,the term combustion point is determined by the technique of PenskyMartens and is defined in DIN (German Industrial Standard) 51758.

Similarly, in the present examples, as well as elsewhere in the presentinvention, the term combustion protection duration (herein sometimesabbreviated by the symbol i is determined also by the Pensky Martenstechnique (defined in same DIN Standard). Time is here taken as theinterval which passes after the opening of the capacitor container untilcombustion occurs. During this interval, the temperature is recorded.

EXAMPLE 1 A flame-retarded, dielectric impregnating fluid is prepared bymixing together to form a single phase liquid the following material (ona weight percent total fluid composition basis):

Component Wt. l. dodecylbenzene 99.8 2. N-tril'luoromethylperfluorooxazine 0.1 3. perfluoroalkylpolyether 0.1

(boiling point 152C) When the fluid is used as the impregnatingdielectric fluid in a capacitor of the type illustrated in FIG. 3, thecapacitor displays a combustion protection time 2,, of about 10 secondsin the temperature range of from about to 300C.

Component 3) used in this Example has the structure:

F CFCHZO CHFCFS and its molecular weight is about 618, its boiling pointis about 152C. and its relative dielectric constant is about 2.6. Thismaterial is substantially noncombustible.

Component 2) has a molecular weight of about 299, a boiling point of5060C. and a relative dielectric constant of about 1.8. This material issubstantially non-combustible.

Component 1) has a combustion point of about 142C., a boiling point ofabout 280300C., and a relative dielectric constant of about 1.8.

EXAMPLE 2 A flame-retarded, dielectric impregnating fluid is prepared bymixing together to form a single phase liquid the following materials(on a 100 weight percent total fluid composition basis):

Component Wt. l. mineral oil 99.8 2. perfluorinated 1,4 0.1dimethylcyclohexane 3. l-trifluoromethyl 0.1

perfluorodecalin When this fluid is charged as the impregnatingdielectric fluid in a capacitor of the type illustrated in FIG. 3, thecapacitor displays a combustion protection time t,, of about 10 secondsin the temperature range of from about 180 to 300C.

Component 3) has a molecular weight of about 512, a boiling point ofabout 160C., and a relative dielectric constant of about 2.0. Thismaterial is substantially non-combustible.

Component 2) has a molecular weight of about 400, a boiling point ofabout 102C and a relative dielectric constant of about 1.9.

Component 1) contains about 56 weight percent parafflnic hydrocarbons,about 29 weight percent naphthalenic hydrocarbons, and about weightpercent aromatic hydrocarbons. This component has a combustion point ofabout 185C., a boiling point of about 300C, and a relative dielectricconstant of about 2.2.

EXAMPLE 3 A flame retarded, dielectric impregnating fluid is prepared bymixing together to form a single phase liquid I the following materialsComponent Wt. l. dioctylsebacate 2. perfluorinatedl,4-dimethylcyclohexane 3. perfluoroalkylpolyether (boiling point 194C)When this fluid is charged as the impregnating dielec tric fluid in acapacitor of this type illustrated in FIG. 3, the capacitor displays acombustion protection time t,, of about 10 seconds in the temperaturerange of from about 250 to 300C.

The component 3), used in this Example has the structure:

F(CFCF) CHFCF;

and its molecular weight is about 784, its boiling point is about 194C,and its dielectric constant is about 2.0. This material is substantiallynoncombustible.

The characteristics of component 2) used in this Example are asdescribed in Example 2.

Component 1) used in this Example has a boiling point somewhat overabout 350C. and a combustion point ofabout 265C.

TABLE I V,,,/Vol-o/oo Perfluorinated Boiling Liquid Point (at indicatedOil temperature 200C 250C 300C Trifluoro- 50-60 0.5 0.25 0.25

methylper fluorohydrooxazine Perfluorinated Dimethyleyclo hexanePerfluoroalkylpoly ether TrifluoromethylperfluorodecalinPerfluoroalkylpoly ether TABLE 2 Boiling Point C Perfluorinated Liquid t/sec at indicated Oil temperature "C 200C 18 The claims are:

l. A capacitor of the regenerative type adapted to have decreasedinflammability comprising:

A. a gas tight and liquid tight housing,

B. at least one capacitive element positioned in said housing eachcapacitive element comprising alternate wound layers of a dielectricumsheet member comprising polyolefin interposed between a pair ofelectrically conductive sheet members each comprising a metalized papersheet, of which at least one is regenerable,

C. spacer means adapted to maintain said capacitive element(s) inspaced, electrically separate relationship to said housing,

D. a pair of electrical current conduit means passin through saidhousing, one of such conduit means interconnecting in each capacitiveelement with one of said conductive sheet members and the other of suchconduit means interconnecting in each capacitive elment with the otherof said conductive sheet members,

E. a dielectric fluid adapted to impregnate said electrically conductivesheet members in each capacitive element and present within said housingin a quantity at least sufficient to impregnate and to surround saidcapacitive element(s) and also to form an excess thereabove with a vaporspace above the level of such fluid in said housing when said capacitoris in a functional position spatially, said vapor space being saturatedwith the vapors of said fluid,

F. each such capacitive element being adapted for self regeneration ofits capacitive capability in the event of a failure thereof in responseto electrical energy applied to said conduit means, and

G. said fluid comprising in homogeneous combination 1. a hydrocarbonliquid having a boiling point in the range of from about 250 to 300C.,and having a combustion point in the range from about 140 to 270C.,

2. a liquid fluorocarbon mixture comprising:

a. at least one first fluorocarbon selected from the group consisting oftrifluoromethyl perfluorohydrooxazine and perfluorinateddimethylcyclohexane,

b. at least one second fluorocarbon selected from the group consistingof a perfluoroalkylpolyether which has a boiling point of about 152C, aperfluoroalkylpolyether which has a boiling point of about 194C, andtrifluoromethyl perfluorodecalin,

c. the weight ratio of said first fluorocarbon to said secondfluorocarbon in any given said fluorocarbon mixture being in the rangeof from about 0.65 z 1 to 1.3 0.5,

3. the weight ratio of said fluorocarbon liquid to said hydrocarbonliquid being in the range from about 0.00025 1 to 0.1 1 with this ratioin any given said fluid being such that in said capacitor the durationof combustion protection is at least about 5 seconds at each of about250C. and about 300C.

2. The capacitor of claim 1 wherein, in said fluid, the duration ofcombustion protection is at least about 5 seconds at each of about 180C.and about 300C.

3. The capacitor of claim 1 wherein, in said fluid, the hydrocarbonliquid is dodecylbenzene, the liquid fluorocarbon mixture comprises assaid first fluorocarbon trifluoromethyl perfluorohydrooxazine, and saidsecond fluorocarbon is selected from the group consisting of aperfluoroalkylpolyether which has a boiling point of about 152C. andtrifluoromethyl perfluorodecaline, and said ratio of said fluorocarbonmixture to said hydrocarbon mixture in any given said fluid being suchthat the duration of combustion protection is at least about 5 secondsat each of about 150C. and about 300C.

4. The capacitor of claim 1, in said fluid, the hydrocarbon liquid isdioctylsebacate, and the liquid fluorocarbon mixture comprises as saidfirst fluorocarbon perfluorinated dimethylcyclohexane and said secondfluorocarbon is selected from the group consisting of aperfluoroalpolyether which has a boiling point of about 152C. and aperfluoroalkylpolyether which has a boiling point of about 194C. andsaid ratio of said fluorocarbon mixture to said hydrocarbon mixture inany given said fluid being such that the duration of combustionprotection is at least about 5 seconds at each of about 250C. and 300C.

5. The capacitor as defined in claim 1, wherein said first fluorocarbonis trifluoromethyl perfluorohydrooxazine and said second fluorocarbon isa perfluoroalkylpolyether which has a boiling point of about 152C.

6. The capacitor as defined in claim 1, wherein said first fluorocarbonis trifluoromethyl perfluorohydrooxazine and said second fluorocarbon isa perfluoroalkylpolyether which has a boiling point of about 194C.

7. The capacitor as defined in claim 1, wherein said first fluorocarbonis trifluoromethyl perfluorohydrooxazine and said second fluorocarbon istrifluoromethyl perfluorohydrooxazine.

8. The capacitor as defined in claim 1, wherein said first fluorocarbonis perfluorinated dimethylcyclohexane and said second fluorocarbon is aperfluoroalkylpolyether which has a boiling point of about 152C.

9. The capacitor as defined in claim 1, wherein said first fluorocarbonis perfluorinated dimethylcyclohexane and said second fluorocarbon is aperfluoroalkylpolyether which has a boiling point of about 194 C.

10. The capacitor as defined in claim 1, wherein said first fluorocarbonis perfluorinated dimethylcyclohexane and said second fluorocarbon is atrifluoromethyl perfluorodecalin.

11. The capacitor as defined in claim 3, wherein said first fluorocarbonis trifluoromethyl perfluorohydrooxazine and said second fluorocarbon isa perfluoroalkylpolyether which has a boiling point of about 152C.

12. The capacitor as defined in claim 3, wherein said first fluorocarbonis trifluoromethyl perfluorohydrooxazine and said second fluorocarbon isa trifluoromethyl perfluorodecalin.

13. The capacitor as defined in claim 3, wherein said first fluorocarbonis perfluorinated dimethylcyclohexane and said second fluorocarbon is aperfluoroalkylpolyether which has a boiling point of about 194C.

14. The capacitor of claim 1, wherein said hydrocarbon liquid isselected from the group consisting of mineral oil, dodecylbenzene, anddioctylsebacate.

15. The capacitor of claim 14, wherein said mineral oil comprises, on aweight percent total mineral oil basis, about 56 weight percentparaffinic constituents, about 29 weight of naphthalenic constituents,and about 15 weight percent aromatic constituents.

16. The capacitor of claim 1, wherein said hydrocarbon liquid is dioctylsebacate.

17. The capacitor of claim 1, wherein said hydrocarbon liquid isdodecylbenzene.

18. The capacitor of claim 1, wherein said polyolefin is polypropylene.

2. The capacitor of claim 1 wherein, in said fluid, the duration ofcombustion protection is at least about 5 seconds at each of about180*C. and about 300*C.
 2. a liquid fluorocarbon mixture comprising: a.at least one first fluorocarbon selected from the group consisting oftrifluoromethyl perfluorohydrooxazine and perfluorinateddimethylcyclohexane, b. at least one second fluorocarbon selected fromthe group consisting of a perfluoroalkylpolyether which has a boilingpoint of about 152*C, a perfluoroalkylpolyether which has a boilingpoint of about 194*C, and trifluoromethyl perfluorodecalin, c. theweight ratio of said first fluorocarbon to said second fluorocarbon inany given said fluorocarbon mixture being in the range of from about0.65 : 1 to 1.3 : 0.5,
 3. the weight ratio of said fluorocarbon liquidto said hydrocarbon liquid being in the range from about 0.00025 : 1 to0.1 : 1 with this ratio in any given said fluid being such that in saidcapacitor the duration of combustion protection is at least about 5seconds at each of about 250*C. and about 300*C.
 3. The capacitor ofclaim 1 wherein, in said fluid, the hydrocarbon liquid isdodecylbenzene, the liquid fluorocarbon mixture comprises as said firstfluorocarbon trifluoromethyl perfluorohydrooxazine, and said secondfluorocarbon is selected from the group consisting of aperfluoroalkylpolyether which has a boiling point of about 152*C. andtrifluoromethyl perfluorodecaline, and said ratio of said fluorocarbonmixture to said hydrocarbon mixture in any given said fluid being suchthat the duration of combustion protection is at least aboUt 5 secondsat each of about 150*C. and about 300*C.
 4. The capacitor of claim 1, insaid fluid, the hydrocarbon liquid is dioctylsebacate, and the liquidfluorocarbon mixture comprises as said first fluorocarbon perfluorinateddimethylcyclohexane and said second fluorocarbon is selected from thegroup consisting of a perfluoroalpolyether which has a boiling point ofabout 152*C. and a perfluoroalkylpolyether which has a boiling point ofabout 194*C. and said ratio of said fluorocarbon mixture to saidhydrocarbon mixture in any given said fluid being such that the durationof combustion protection is at least about 5 seconds at each of about250*C. and 300*C.
 5. The capacitor as defined in claim 1, wherein saidfirst fluorocarbon is trifluoromethyl perfluorohydrooxazine and saidsecond fluorocarbon is a perfluoroalkylpolyether which has a boilingpoint of about 152*C.
 6. The capacitor as defined in claim 1, whereinsaid first fluorocarbon is trifluoromethyl perfluorohydrooxazine andsaid second fluorocarbon is a perfluoroalkylpolyether which has aboiling point of about 194*C.
 7. The capacitor as defined in claim 1,wherein said first fluorocarbon is trifluoromethyl perfluorohydrooxazineand said second fluorocarbon is trifluoromethyl perfluorohydrooxazine.8. The capacitor as defined in claim 1, wherein said first fluorocarbonis perfluorinated dimethylcyclohexane and said second fluorocarbon is aperfluoroalkylpolyether which has a boiling point of about 152*C.
 9. Thecapacitor as defined in claim 1, wherein said first fluorocarbon isperfluorinated dimethylcyclohexane and said second fluorocarbon is aperfluoroalkylpolyether which has a boiling point of about 194* C. 10.The capacitor as defined in claim 1, wherein said first fluorocarbon isperfluorinated dimethylcyclohexane and said second fluorocarbon is atrifluoromethyl perfluorodecalin.
 11. The capacitor as defined in claim3, wherein said first fluorocarbon is trifluoromethylperfluorohydrooxazine and said second fluorocarbon is aperfluoroalkylpolyether which has a boiling point of about 152*C. 12.The capacitor as defined in claim 3, wherein said first fluorocarbon istrifluoromethyl perfluorohydrooxazine and said second fluorocarbon is atrifluoromethyl perfluorodecalin.
 13. The capacitor as defined in claim3, wherein said first fluorocarbon is perfluorinated dimethylcyclohexaneand said second fluorocarbon is a perfluoroalkylpolyether which has aboiling point of about 194*C.
 14. The capacitor of claim 1, wherein saidhydrocarbon liquid is selected from the group consisting of mineral oil,dodecylbenzene, and dioctylsebacate.
 15. The capacitor of claim 14,wherein said mineral oil comprises, on a 100 weight percent totalmineral oil basis, about 56 weight percent paraffinic constituents,about 29 weight of naphthalenic constituents, and about 15 weightpercent aromatic constituents.
 16. The capacitor of claim 1, whereinsaid hydrocarbon liquid is dioctyl sebacate.
 17. The capacitor of claim1, wherein said hydrocarbon liquid is dodecylbenzene.
 18. The capacitorof claim 1, wherein said polyolefin is polypropylene.